As a method for imparting water/oil repellency to the surface of an article (such as a fiber product), a method of dipping the article in a water/oil repellent composition composed of an emulsion having, dispersed in an aqueous medium, a copolymer having structural units based on a monomer having a polyfluoroalkyl group (hereinafter referred to as a Rf group) and drying the article has been known.
In recent years, in view of the improvement in work environment and the energy saving, an article dipped in a water/oil repellent composition is required to be dried at room temperature (hereinafter drying at room temperature will be referred to as air-drying) in some cases. However, in a case where an article dipped in a water/oil repellent composition is air-dried, the article will be insufficient in the water/oil repellency (hereinafter the water/oil repellency of an article in the case of air-drying will be referred to as post-air-drying water/oil repellency).
As a water/oil repellent composition which can impart post-air-drying water/oil repellency to the surface of an article, for example, the following water/oil repellent composition has been proposed.
A water/oil repellent composition comprising a copolymer (A) having (I) structural units based on a monomer having an Rf group, (II) structural units based on a monomer having a urethane or urea bond, (III) structural units based on a monomer, the homopolymer of which has a glass transition temperature of at most 50° C., (IV) structural units based on a monomer having a hydrophilic group and (V) structural units based on a monomer having a chlorine atom, and a film-forming assistant (B), dispersed in an aqueous medium (Patent Document 1).
By the way, recently, EPA (US Environmental Protection Agency) has pointed out that a compound having a perfluoroalkyl group (a perfluoroalkyl group will be hereinafter referred to as a RF group) having at least 7 carbon atoms is likely to be decomposed in the environment or in the body, and the decomposition product is likely to be accumulated, i.e. it presents a high environmental impact. Therefore, a water/oil repellent composition comprising a copolymer which has structural units based on a monomer having a RF group having at most 6 carbon atoms, and has no structural units based on a monomer having a RF group having at least 7 carbon atoms, has been required.
However, in the water/oil repellent composition as disclosed in Patent Document 1, if the number of carbon atoms in the Rf group of the monomer in (I) is at most 6, the post-air-drying water/oil repellency of the article is insufficient.